This invention relates to a pneumatic pressure conveyor for fine material, with two superimposed pressure vessels, wherein the closable material inlet aperture of the upper pressure vessel is connected to a feeder for the material and the lower section of the lower pressure vessel is connected to a pneumatic feed conduit, and wherein at least the upper pressure vessel has a material aerating cone pressurisable by gas, the outlet aperture of said cone being connected by a valve member to the inlet aperture of the other pressure vessel in such a manner that when the upper vessel is pressurized and the inlet aperture to the vessel is closed, the valve member is opened in order to fill the lower vessel, and wherein both pressure vessels are connected to pressure conduits or pressure equalising conduits.
Pneumatic pressure conveyors are very widely known which comprise only one pressure vessel and hence can only expel fine material from the pressure vessel discontinously, since the vessel must first be filled, then closed and finally pressurised so that the material can be pneumatically expelled from the pressure vessel.
In order to be able to convey with pneumatic pressure conveyors as continuously as possible, various constructions have therefore been provided (see for instance German DAS No. 1212871 and German OLS No. 1903539) wherein two pressure vessels are disposed one above the other in the manner initially described and joined together. With these constructions, while the fine material in the lower pressure vessel is being pneumatically extracted, with the outlet aperture closed and the inlet aperture opened in the upper pressure vessel, it is possible for further fine material to reach the pressure conveyor and be received in the upper pressure vessel. When the upper pressure vessel is sufficiently filled, its inlet aperture is then closed, the vessel is pressurised (so that approximately the same pressure prevails in both pressure vessels) and then its outlet aperture is opened, so that fresh material is supplied to the lower pressure vessel from which material can be continuously extracted.
The difficulty with this known device is that, at least in the upper pressure vessel, the fine material often tends to form bridges, which hinder or prevent the pneumatic conveyance. To alleviate this difficulty, the known pressure conveyors have been altered by providing at least the upper pressure vessel with a material-aerating cone pressurisable by gas, whose casing has portions that are porous, such as for instance ceramic plates, sintered metal plates and the like, through which the aerating gas (e.g. air) is fed into the container. This measure has ind ed proved satisfactory in ordinary mixing and storage silos, but cannot achieve satisfactory loosening of the material present in the pressure vessel, this being mainly due to the fine material undergoing marked compaction during the pressure equalisation.